High-performance liquid chromatographic assay with fluorescence detection for the evaluation of inhibitors against fatty acid amide hydrolase

Synthesis, activity and metabolic stability of propan-2-one substituted tetrazolylalkanoic acids as dual inhibitors of cytosolic phospholipase A2α and fatty acid amide hydrolase

The serine hydrolases cytosolic phospholipase A2α (cPLA2α) and fatty acid amide hydrolase (FAAH) are interesting targets for the development of new anti-inflammatory and analgesic drugs. Structural modifications of a potent dual inhibitor with a propan-2-one substituted tetrazolylpropionic acid moiety led to compounds with also nanomolar activity against both enzymes but better physicochemical properties. The structure-activity relationships showed that the variations had partially divergent effects on the inhibitory activity of the compounds towards cPLA2α and FAAH reflecting differences in the binding mode to the enzymes. Furthermore, the metabolic stability of the target structures was investigated in vitro.

HPLC fluorescence assay for measuring the activity of NAPE-PLD and the action of inhibitors affecting this enzyme

N-Acyl phosphatidylethanolamine-hydrolyzing phospholipase D (NAPE-PLD) is the major enzyme for the biosynthesis of the endocannabinoid anandamide. The role of NAPE-PLD in various physiological and pathophysiological conditions is currently under investigation. For example, the enzyme might be involved in the control of neuronal activity, embryonic development and pregnancy, and prostate cancer. We synthesized a novel NAPE-PLD substrate with a fluorogenic pyrene substituent at the N-acyl residue as tool compound for studying this enzyme. As shown by HPLC with fluorescence detection, in rat brain microsomes the substrate was transformed into the expected pyrene-labeled N-acylethanolamine (NAE), but minor amounts of three by-products could also be detected. In the presence of pan-serine hydrolase and secretory phospholipase A₂ inhibitors, the generation of these compounds, whose identity was verified using reference substances, was abolished. Based on these results, a method for determining the activity of NAPE-PLD was developed, validated, and applied to evaluate the action of known inhibitors of this enzyme. With human sperm, it was shown that the fluorescent substrate can also be used to study NAPE metabolism in intact cells.

HPLC fluorescence assay for measuring the activity of diacylglycerol lipases and the action of inhibitors thereof

1,2-Diacylglycerol lipases (DAGLs) are the most important enzymes for the biosynthesis of the endocannabinoid 2-arachidonoylglycerol (2-AG), and their role in various pathophysiological conditions is currently under investigation. We synthesized a new 1,2-diacylglycerol substrate for these enzymes with a fluorogenic 4-(pyren-1-yl)butanoyl residue in sn-2 position. Using the fluorescent substrate, we measured DAGL activity in rat liver S9 fraction and brain microsomes. To this end, 2-acylglycerol release was directly determined via HPLC and fluorescence detection without further sample clean-up. The method was used to evaluate the action of several known DAGL inhibitors. These showed partly significant differences in their inhibitory effect on DAGLs in liver versus brain preparations. The method was verified by measuring the IC₅₀ values for a subset of inhibitors by HPLC and single-quad MS detection using the deuterated natural DAGL substrate 1-stearoyl-2-arachidonoyl-sn-glycerol-d₈. DAGL activity could also be measured with the new pyrene-labeled substrate by HPLC and UV instead of fluorescence detection, if larger quantities of the samples were injected into the HPLC system. Furthermore, using intact human sperm, we show that the substrate is also converted by DAGL enzymes in human cells.

Hexafluoroisopropyl carbamates as selective MAGL and dual MAGL/FAAH inhibitors: biochemical and physicochemical properties

A series of hexafluoroisopropyl carbamates with indolylalkyl‐ and azaindolylalkyl‐substituents at the carbamate nitrogen was synthesized and evaluated for inhibition of the endocannabinoid degrading enzymes fatty acid amide hydrolase (FAAH) and monoacylglycerol lipase (MAGL). The synthesized derivatives with butyl to heptyl spacers between the heteroaryl and the carbamate moiety were inhibitors of both enzymes. For investigated compounds in which the alkyl chain was partially incorporated into a piperidine ring, different results were obtained. Compounds with a methylene spacer between the piperidine ring and the heteroaromatic system were found to be selective MAGL inhibitors, while an extension of the alkyl spacer to two to four atoms resulted in dual inhibition of FAAH/MAGL. The only small change in enzyme inhibitory activity with variation of the heteroaromatic system indicates that the reactive hexafluoroisopropyl carbamate group is mainly responsible for the strength of the inhibitory effect of the compounds. Selected derivatives were also tested for hydrolytic stability in aqueous solution, liver homogenate and blood plasma as well as for aqueous solubility and for permeability in a Caco‐2 cell model. Some compounds showed a slightly higher MAGL inhibitory effect than the known selective MAGL inhibitor ABX‐1431 and also partly surpassed this substance with regard to certain physicochemical and biochemical properties such as water solubility and cell permeability.

Aryl N-[ω-(6-Fluoroindol-1-yl)alkyl]carbamates as Inhibitors of Fatty Acid Amide Hydrolase, Monoacylglycerol Lipase, and Butyrylcholinesterase: Structure-Activity Relationships and Hydrolytic Stability

A series of aryl N-[ω-(6-fluoroindol-1-yl)alkyl]carbamates with alkyl spacers of varying lengths between the indole and the carbamate group and with differently substituted aryl moieties at the carbamate oxygen were synthesized and tested for inhibition of the pharmacologically interesting serine hydrolases fatty acid amide hydrolase (FAAH), monoacylglycerol lipase (MAGL), butyrylcholinesterase (BuChE), and acetylcholinesterase (AChE). Furthermore, the chemical stability in an aqueous solution and the metabolic stability toward esterases in porcine liver homogenate and porcine blood plasma were determined. While most of the synthesized derivatives were potent inhibitors of FAAH, a considerable inhibition of MAGL and BuChE was elicited only by compounds with a high carbamate reactivity, as evidenced by a significant hydrolysis of these compounds in an aqueous solution. However, the high inhibitory potency of some compounds toward MAGL and BuChE, especially that of the ortho-carboxyphenyl derivative 37, could not be explained by chemical reactivity alone. Several of the carbamates studied possessed varying degrees of stability toward esterases from liver and blood plasma. In some cases, marked inactivation by the pseudo-esterase activity of plasma albumin was observed. Mass spectrometric studies showed that such carbamates formed covalent bonds with albumin at several sites.

Characterization of fatty acid amide hydrolase activity by a fluorescence-based assay

Fatty acid amide hydrolase (FAAH) is involved in many human diseases, particularly cancer, pain and inflammation as well as neurological, metabolic and cardiovascular disorders. Therefore, FAAH is an attractive target for the development of low-molecular-weight inhibitors as therapeutics, which requires robust assays that can be used for high-throughput screening (HTS) of compound libraries. Here, we report the development of a fluorometric assay based on FAAH's ability to effectively hydrolyze medium-chain fatty acid amides, introducing N-decanoyl-substituted 5-amino-2-methoxypyridine (D-MAP) as new amide substrate. D-MAP is cleaved by FAAH with an 8-fold larger specificity constant than the previously reported octanoyl-analog Oc-MAP (V_max/K_m of 1.09 and 0.134 mL min^-1 mg^-1, respectively), with both MAP derivatives possessing superior substrate properties and much increased aqueous solubility compared to the respective p-nitroaniline compounds D-pNA and Oc-pNA. The new assay with D-MAP as substrate is highly sensitive using a lower enzyme concentration (1 μg mL^-1) than literature-reported fluorimetric FAAH assays. In addition, D-MAP was validated in comparison to the substrate Oc-MAP for the characterization of FAAH inhibitors by means of the reference compounds URB597 and TC-F2 and was shown to be highly suitable for HTS in both kinetic and endpoint assays (Z' factors of 0.81 and 0.78, respectively).

Cross-validated stable-isotope dilution GC-MS and LC-MS/MS assays for monoacylglycerol lipase (MAGL) activity by measuring arachidonic acid released from the endocannabinoid 2-arachidonoyl glycerol

2-Arachidonoyl glycerol (2AG) is an endocannabinoid that activates cannabinoid (CB) receptors CB1 and CB2. Monoacylglycerol lipase (MAGL) inactivates 2AG through hydrolysis to arachidonic acid (AA) and glycerol, thus modulating the activity at CB receptors. In the brain, AA released from 2AG by the action of MAGL serves as a substrate for cyclooxygenases which produce pro-inflammatory prostaglandins. Here we report stable-isotope GC-MS and LC-MS/MS assays for the reliable measurement of MAGL activity. The assays utilize deuterium-labeled 2AG (d₈-2AG; 10μM) as the MAGL substrate and measure deuterium-labeled AA (d₈-AA; range 0-1μM) as the MAGL product. Unlabelled AA (d₀-AA, 1μM) serves as the internal standard. d₈-AA and d₀-AA are extracted from the aqueous buffered incubation mixtures by ethyl acetate. Upon solvent evaporation the residue is reconstituted in the mobile phase prior to LC-MS/MS analysis or in anhydrous acetonitrile for GC-MS analysis. LC-MS/MS analysis is performed in the negative electrospray ionization mode by selected-reaction monitoring the mass transitions [M-H]^-→[M-H - CO₂]^-, i.e., m/z 311→m/z 267 for d₈-AA and m/z 303→m/z 259 for d₀-AA. Prior to GC-MS analysis d₈-AA and d₀-AA were converted to their pentafluorobenzyl (PFB) esters by means of PFB-Br. GC-MS analysis is performed in the electron-capture negative-ion chemical ionization mode by selected-ion monitoring the ions [M-PFB]^-, i.e., m/z 311 for d₈-AA and m/z 303 for d₀-AA. The GC-MS and LC-MS/MS assays were cross-validated. Linear regression analysis between the concentration (range, 0-1μM) of d₈-AA measured by LC-MS/MS (y) and that by GC-MS (x) revealed a straight line (r²=0.9848) with the regression equation y=0.003+0.898x, indicating a good agreement. In dog liver, we detected MAGL activity that was inhibitable by the MAGL inhibitor JZL-184. Exogenous eicosatetraynoic acid is suitable as internal standard for the quantitative determination of d₈-AA produced from d₈-2AG by hepatic MAGL activity. The formation of d₈-prostaglandin E₂ by the consecutive catalytic action of recombinant MAGL on d₈-2AG and recombinant cyclooxygenase-2 (COX) on d₈-AA was demonstrated by GC-MS/MS.

(Indolylalkyl)piperidine carbamates as inhibitors of fatty acid amide hydrolase (FAAH)

A series of phenyl 4-[(indol-1-yl)alkyl]piperidine carbamates was synthesized and tested for inhibition of the endocannabinoid degrading enzyme fatty acid amide hydrolase (FAAH) and for metabolic stability in rat liver S9 fractions and porcine blood plasma. Structure-activity relationship studies revealed that variation of the length of the alkyl spacer connecting the indole and the piperidine heterocycle, introduction of substituents into the indole ring, replacement of the piperidine by a piperazine scaffold as well as opening of the piperidine ring system affect activity significantly. The metabolic stability of this compound class proved to be significantly higher than that of corresponding phenyl N-(indol-1-ylalkyl)carbamates.

1-Heteroarylpropan-2-ones as inhibitors of fatty acid amide hydrolase: Studies on structure-activity relationships and metabolic stability

The serine hydrolase fatty acid amide hydrolase (FAAH) catalyzes the degradation of the endocannabinoid anandamide, which possesses analgesic and anti-inflammatory effects. A new series of 1-heteroarylpropan-2-ones was synthesized and evaluated for FAAH inhibition. Structure-activity relationship studies revealed that 1H-benzotriazol-1-yl, 1H-7-azabenzotriazol-1-yl, 1H-tetrazol-1-yl and 2H-tetrazol-2-yl substituents have the highest impact on inhibitory potency. Furthermore, attempts were made to increase the limited metabolic stability of the ketone functionality of these compounds towards metabolic reduction by introduction of shielding alkyl substituents in proximity of this serine reactive group.

1-(5-Carboxyindazol-1-yl)propan-2-ones as dual inhibitors of cytosolic phospholipase A2α and fatty acid amide hydrolase: bioisosteric replacement of the carboxylic acid moiety

Indazole-5-carboxylic acids with 3-aryloxy-2-oxopropyl residues in position 1 were previously reported to be potent dual inhibitors of cytosolic phospholipase A₂α (cPLA₂α) and fatty acid amide hydrolase (FAAH). In continuation of our structure-activity studies on cPLA₂α and FAAH inhibitors, a number of derivatives of these substances characterized by bioisosteric replacement of the carboxylic acid functionality by inverse amides, sulfonylamides, carbamates and ureas were prepared. The biological evaluation of the obtained compounds showed that the carboxylic acid functionality of the lead compounds is of special importance for a pronounced inhibition of cPLA₂α and FAAH.

Structure-activity relationship studies on 1-heteroaryl-3-phenoxypropan-2-ones acting as inhibitors of cytosolic phospholipase A2α and fatty acid amide hydrolase: replacement of the activated ketone group by other serine traps

Cytosolic phospholipase A2α (cPLA2α) and fatty acid amide hydrolase (FAAH) are serine hydrolases. cPLA2α is involved in the generation of pro-inflammatory lipid mediators, FAAH terminates the anti-inflammatory effects of endocannabinoids. Therefore, inhibitors of these enzymes may represent new drug candidates for the treatment of inflammation. We have reported that certain 1-heteroarylpropan-2-ones are potent inhibitors of cPLA2α and FAAH. The serine reactive ketone group of these compounds, which is crucial for enzyme inhibition, is readily metabolized resulting in inactive alcohol derivatives. In order to obtain metabolically more stable inhibitors, we replaced this moiety by α-ketoheterocyle, cyanamide and nitrile serine traps. Investigations on activity and metabolic stability of these substances revealed that in all cases an increased metabolic stability was accompanied by a loss of inhibitory potency against cPLA2α and FAAH, respectively.

ω-Heteroarylalkylcarbamates as inhibitors of fatty acid amide hydrolase (FAAH)

A series of heteroaryl-substituted alkylcarbamates have been synthesized and evaluated for their inhibitory potency against fatty acid amide hydrolase (FAAH).

Magnolia Extract, Magnolol, and Metabolites: Activation of Cannabinoid CB2 Receptors and Blockade of the Related GPR55

The bark of Magnolia officinalis is used in Asian traditional medicine for the treatment of anxiety, sleeping disorders, and allergic diseases. We found that the extract and its main bioactive constituents, magnolol and honokiol, can activate cannabinoid (CB) receptors. In cAMP accumulation studies, magnolol behaved as a partial agonist (EC50 = 3.28 μM) with selectivity for the CB2 subtype, while honokiol was less potent showing full agonistic activity at CB1 and antagonistic properties at CB2. We subsequently synthesized the major metabolites of magnolol and found that tetrahydromagnolol (7) was 19-fold more potent than magnolol (EC50 CB2 = 0.170 μM) exhibiting high selectivity versus CB1. Additionally, 7 behaved as an antagonist at GPR55, a CB-related orphan receptor (K B = 13.3 μM, β-arrestin translocation assay). Magnolol and its metabolites may contribute to the biological activities of Magnolia extract via the observed mechanisms of action. Furthermore, the biphenylic compound magnolol provides a simple novel lead structure for the development of agonists for CB receptors and antagonists for the related GPR55.

Design, synthesis and evaluation of polar head group containing 2-keto-oxazole inhibitors of FAAH

2-α-Keto oxazoles containing polar head groups in their C5-side chains were designed as fatty acid amide hydrolase (FAAH) inhibitors. Variation in the spacer length resulted in submicromolar α-keto-oxazole FAAH inhibitor (IC(50)=436 nM) presenting electrostatic stabilizing interactions between its polar head group contained in the C5-side chain and the hydrophilic pocket of the enzyme.

Cardiac mortality is associated with low levels of omega-3 and omega-6 fatty acids in the heart of cadavers with a history of coronary heart disease

The benefits of omega-3 (ie, eicosapentaenoic acid and docosahexaenoic acid [DHA]) and omega-6 (ie, linoleic acid and arachidonic acid [AA]) fatty acids on reducing cardiac mortality are still debated. In this study, we tested the hypothesis that high levels of omega-3 and omega-6 fatty acids in heart tissues are associated with low cardiac mortality in Thai cadavers. One hundred fresh cadavers were examined in this study. The cause of death, history of coronary heart disease (CHD), and fish consumption habits were obtained from death certificates, cadaver medical record profiles, and a questionnaire to a person who lived with the subject before death. In each cadaver, biopsies of cardiac tissues were taken from the interventricular septum for measurement of fatty acid. Of the 100 cadavers (average age, 69 +/- 13 years), 60 were men. The frequency of fish consumption was directly associated with omega-3 and omega-6 fatty acids in heart tissues (P < .01). History of CHD and cause of death (cardiac vs noncardiac) were not significantly associated with levels of omega-3 or omega-6 fatty acids. However, in cadavers with a history of CHD, high levels of omega-3 and omega-6, particularly DHA and AA, were associated with low cardiac mortality (P < .05). Fish consumption is associated with levels of omega-3 and omega-6 fatty acids in heart tissues. Although omega-3 and omega-6 fatty acids are not associated with cardiac mortality in the overall studied population, their low levels (especially DHA and AA) in heart tissues are associated with high cardiac mortality in cadavers with a history of CHD.